SHORT BEAKED COMMON DOLPHIN

ENDANGERED IN THE MEDITERRANEAN SEA

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The short-beaked common dolphin Delphinus delphis is a small cetacean species with a wide distribution. Like most other cetaceans, however, it is not panmictic and occurs as a series of geographically separate populations

In the Mediterranean Sea it is found both in the pelagic and in the neritic environment, often sharing the former with striped dolphins and the latter with common bottlenose dolphins. Neritic communities seem to show relatively high levels of site fidelity, while little is known about the movements and range patterns of offshore animals.

Literature, photographic documentation, and osteological collections indicate that the common dolphin used to be common - thence its name - throughout the Mediterranean Sea, however the species has experienced a dramatic decline in numbers during the last few decades, and has almost completely disappeared from large portions of its former range including the northern Adriatic Sea and the Ligurian Sea.

In 2003 the Mediterranean common dolphin 'subpopulation' was listed as endangered in the IUCN Red List of Threatened Animals, based on criterion A2, which refers to a 50% decline in abundance over the last three generations, the causes of which 'may not have ceased or may not be understood or may not be reversible' (http://www.redlist.org).

Short-beaked common dolphins in the Mediterranean have undergone a remarkable drop in abundance and have almost completely disappeared from large portions of their former range. A number of interacting factors may have played a role in the decline of common dolphins in the Mediterranean, ranging from natural fluctuations to the impact of human activities. Some of the human-induced threats - based on the available evidence - are most likely to be implicated in the species' decline.

These include factors as diverse as prey depletion, contamination by xenobiotics, direct killing, fishery bycatch and global climate change.

Other potential threats to Mediterranean common dolphins include disturbance by recreational vessel traffic, noise from shipping, mineral prospecting (seismic) and military sonar, and oil pollution.

Although potentially pervasive, these threats remain poorly characterized or have yet to be linked with specific effects on common dolphins in the Mediterranean or elsewhere.

This impressive situation in the Mediterranean Sea underline that the fate of remaining animals will likely depend upon precautionary action and the adoption of precise conservation measures to prevent further decline. However, it is important that any long or short-term management decisions that have an impact on either the dolphins or their habitat are made with the support of detailed and current scientific information

The waters of Ischia have been listed in the last IUCN Cetacean Action Plan (Reeves et al., 2003) as critical habitat for the endangered short beaked common dolphins.

In the study area, the presence of common dolphin population off the northern coast of the island, has been consistently documented since 1997. This is the only common dolphin community monitored in the Italian Seas.

The animals were sighted on a seasonal basis, mostly in the summer, over the submarine canyon of Cuma, a highly productive marine area characterized by significant pelagic biodiversity and multispecies associations. From 1997 to 2000 the mean depth of common dolphin sightings was 164.5m, (±101.8 SD; min 50 m, max 630 m) and the average distance form the nearest coast was 3.5 km. (±2,5 SD; min 0.7 km, max 10 km).

Since 2003, 79 individuals were photoidentified. Of these 79, 77.2% (n=61) of them remained unsexed, 21.5% were females (n=17) and 1% were males (n=1). Many of these identified dolphins (n=47, corresponding to 59%) were re-sighted over the study period, indicating a high degree of residency in the analyzed area.

Breeding activities are often observed, and calves are always present in one or more of the group sub-units, suggesting that, during summer months, the species uses the area also as a breeding ground.

Sighted groups are relatively large (mean=65.5, SD=23.94, n=41, range 35-100 individuals) and often observed in association with striped dolphins (Stenella coeruleoalba), particularly during surface feeding targeting shoaling prey.

Surface feeding occurs frequently and the Atlantic saury Scomberesox saurus (a seasonal fish that is highly valued on local markets) is a typical prey of common dolphins.

Local fishermen claim that co-operative fishing may occur in the area, with fishermen taking advantage of fish aggregations that are actively schooled by short-beaked common dolphins near the surface. In the past, fish rewards were offered to the dolphins in reciprocation. Based on interviews conducted locally, the skipper fishery fleet has decreased by one order of magnitude in the last two decades due to declined fish stocks.